Assessment of Groundwater Quality in Shallow Aquifers in Jaffna Peninsula

Transcription

1 Assessment of Groundwater Quality in Shallow Aquifers in Jaffna Peninsula M.S.M. Hidayathulla* and G.R.R. Karunaratna Water Resources Board, 2A, Hector Kobbekaduwa Avenue, Colombo 7 * E mail: mhmohameds@yahoo.co.uk 1. Introduction Jaffna Peninsula has lesser percentage of surface water sources because of its karstic nature and flat terrain. Whole peninsula depends mainly on its groundwater source for their survival. Groundwater source is recharged by north-east monsoon in the month of November to February. Nowadays water borne diseases which are induced by Agricultural and Anthropological activities are widely spread in Jaffna Peninsula. Therefore, the need for groundwater monitoring is important for the peninsula. Study area is covered by 08 divisional secretariats of Sandilipay, Tellipallai, Point Pedro, Maruthankerny, Kopay, Uduvil (Chunnagam), Chankanai and Karaveddy. Most of the area is covered with cultivation of vegetables, fruits, paddy lands and banana. In these divisions 156 monitoring wells were selected in dry season of the year Sample collection was done scientifically. It is a long term monitoring project to identify the ground water occurrence and quality distribution. Shallower and deeper aquifers are encountered in these areas. In order to fulfil these requirements the following steps are necessary to establish. Establishment of Groundwater Monitoring Network Development of groundwater model for the region Study the spatial variation of water quality of the area Preparation of groundwater vulnerability maps and reports To incorporate land use and land management practices. 2. Study Area Jaffna Peninsula which is the northernmost tip of Sri Lanka has a source of groundwater stored in the sub terrain layer of limestone. No perennial rivers or surface drainage systems, but having one seasonal river Valukki Aru. It is active in wet season, traverses SE from its origin in the central Mallakam region, having several irrigated schemes depending largely on salt water exclusion barrages in the Araly outfall area. The peninsula has an extent of 260,000 acres with a population of 831,112 (1981, Census). But the study area is restricted for only eight DS divisions. Sustainable utilisation of groundwater with Morphology of the area is almost flat and the suitable regulations and operational plans based area around Tellipalai where the elevation on the hydrogeological and geochemical reaches up to 11 m above M.S.L. From here it conditions of the aquifers existed in the region. slopes gently towards the south and South East but to the North the elevations tend to drop Copyright 2013 GSSL 109

2 abruptly as the sea is reached, giving rise to marginal low cliffs. The general lithology of the soil is fine to medium grained. The Jaffna peninsula is mainly underlain by Miocene Limestone (Figure 1). Morphology of the area is almost flat and the area around Tellipalai where the elevation reaches up to 11 m above M.S.L. From here it slopes gently towards the south and South East but to the North the elevations tend to drop abruptly as the sea is reached, giving rise to marginal low cliffs. The soil is fine to medium grained.. This limestone is capped in places by thin layers of residual soil belonging to the Pliocene-Pleistocene Period and lagoonal and Eustrine deposits like brown sands and loams, windblown sands and coral reefs belonging to the Quaternary Period. Geographically, the limestones are exposed at the north central part of the Peninsula, extending in a NNE to SSW direction from Urumpirai to Palali. Bordering this, on the western side are patches of red earth formations. Encompassing these two formations, there is a brown sand formation which occupies a larger area on the western side than on the eastern side. Enclosing these, along the western coast and in the lagoonal areas the lagoonal deposits exist. The area east of the lagoon are occupied mainly by brown sandy loams in the south and sand dunes in the north along the eastern coast of the Peninsula, stretching from Thumpalai to Nagarkovil and beyond to Iyakkachchi. Recent coral reefs are found along the northern coasts of the peninsula. 3. Data Collection and Analyses Initially, preliminary data and information of Figure 1 - Geology of Jaffna Peninsula 110 Copyright 2013 GSSL

3 the area were collected from various organizations and studied for the selection of monitoring points (Figure 2). Then we met the Assistant Directors of Planning of the DS divisions and discussed with them about the groundwater issues in their divisions. They provided some well locations with some issues which were reported by the people as having problems. Also we met most of the GSs of the area and collected available data as we go. Based on the data, reported issues were identified by talking to people in different GN divisions, as well as measurements of some physical and chemical parameters. Locations of wells were located by using GPS. Most of these wells are used for drinking and domestic (Electric conductivity), P H, water depth and well diameter were measured. Samples were collected for further analysis with proper preservations. Selected well locations are shown here. Spot measurement for EC, TDS and Salinity of the water samples were measured by using digital conductivity meter. Nitrate and phosphate were measured in situ in the DR/890 Colourimeter using powder pillow method. Water samples were brought to the chemical laboratory of Water Resources Board Jaffna for further chemical analysis. The procedure of the analysis was based on Sri Lankan Standard 614 (1983). Water samples were analyzed for Chloride by using Silver Nitrate Titration method (Argento metric method), bicarbonate by titrimetric method. Sulphate, fluoride, turbidity, colour, and total iron were measured in DR/890 Colourimeter. Cations and Heavy metals were determined by Atomic Absorption Spectroscopy. Interpolated spatial distribution of the Groundwater quality for the dry season 2012 (by Inverse Distance Weighted method using ArcGIS 9.3 software) implies that temporal variations of quality distribution patterns (Figure 3). Figure 2 - Sampling points of study area purposes while some are Agro wells and very few are abandoned. Geophysical surveys done at selected locations to study the sub surface conditions using 1-D resistivity methods by ABEM 1000 Resistivity meter. Also Test pumping was started targeting different aquifer types in the area and data to be analysed to estimate the aquifer parameters. In those selected wells, hydro chemical analysis was done on spot for nitrate, phosphate, salinity and TDS. Also physical parameters such as EC 4. Results and Discussion In the locations where samples were collected, wells having its age more than 30 years to 150 Copyright 2013 GSSL 111

4 years exist. The appearance of the water is very clear in almost all the wells. P H values range in between 6.93 to Higher P H value was observed in the wells in coastal areas, especially in sand dune areas in eastern cost. Electric conductivity values are ranging between 99.3 µs/cm and 8820 µs/cm. High values were observed in the coastal area in which wells were constructed in Estuarine deposit while lesser values were from the very shallow wells in sand dune areas in east coast. TDS varies in between 2.43mg/L to 3940 mg/l. pits are near to the wells. In agricultural practicing areas in the red bed region, according to the statement of the senior citizens, they are still in a position to use chemical fertiliser in terms of their high amount of harvesting. The farmers are cultivating vegetables such as onion, beet, chilli, curry chilli, green gram and sesame. After harvesting they use other crops such as jute to fertile the land. In home gardens people grow it. Most of their growing periods they use these as compost for their field but in a stage before harvesting, they had to use nearly 10 to 12 kg for quarter acre as well as ammonia Figure 3 Distribution of Water quality Parameters in Jaffna Peninsula Nitrate level is ranging in from 0 to 15.5 mg/l. It is high in cultivation areas because of the use of artificial fertiliser and also where the toilet in a high level. Phosphate values range in between 0 to and 25 mg/l. One of the major limitations to the 112 Copyright 2013 GSSL

5 fieldwork in the study area was the lack of enough hydraulic head data and water quality analysis data in the limestone aquifer due to the lack of monitoring boreholes. Therefore study was mostly restricted to shallow aquifer system. Some high security zones cannot be accessed and sampling was not done in those particular areas for this quality assessment. 5. Conclusions Jaffna Miocene limestone is the principle source of water storage in the Jaffna Peninsula. The shallow aquifer of the peninsula occurs with the channels and cavities (karsts) of this Miocene limestone. Visible karst features include sink holes and solution caverns. According to the results of water samples, groundwater of the study area is polluted due to heavy agricultural practices. Mainly in shallow aquifer groundwater in some part of Jaffna peninsula is totally polluted by nitrate (eg. Kondavil to Kopay area). The usage of excess amount of nitrogen fertiliser and pesticides, weedicides, high population density and shallow groundwater table are the major reasons for this issue. Chunnagam, Kopay and Kondavil areas (red bed areas) are identified as most nitrate areas among other study areas, as well as the numbers of stomach cancer patients are reported in these regions. The farmers in these areas should be encouraged to use access amount of organic composts instead of using higher amount of Nitrogen fertilisers, pesticides and weedicides. The wells which are located very near to the lagoon are totally contaminated by salt water. The over extraction of groundwater also creates the salt water intrusion. The best groundwater source is identified in sand dune aquifer (Vadamarachchi east area up to Iyakkachchi). Freshwater lens and deepen sea could be the reasons for that. This aquifer should be protected from pollution and over extraction. 5. Acknowledgements The authors would like to thank all the supporting staff of Water Resources Board of Sri Lanka for their contribution to facilitate this research work. 6. References Arumugam, S. (1974). Geology and Groundwater Resources in Northwest Ceylon: Studies on Groundwater in Sri Lanka (Ceylon). Water Resources Board, Colombo.p.36. Balendran, V.S., Sirimanne, C.H.L. and S. Arumugam. (1968). Groundwater in Jaffna. Water Resources Board, Colombo. p. 35. Carmelita Nishanthiny, Thushyanthy, T. Barathithasan and Saravanan. (2010). Irrigation Water Quality Based on Hydro Chemical Analysis, Jaffna, Sri Lanka. American-Eurasian J. Agric. & Environ. Sci., Vol. 7 (1), p Rajasooriyar L., Mathavan V., Dharmagunawardhane H.A.D. & Nandakumar V (2002). Groundwater quality in the Valigamam Region of the Jaffna Peninsula, Sri Lanka. Geological Society, London, Special Publications; Vol. 193, p Nagarajah, S., Emerson, B.N., Abeykoon, and Yogalingam, S. (1988). Water quality of some wells in Jaffna and Kilinochchi with special reference to nitrate pollution. Tropical Agriculturalist, Vol. 144, p Nanthani T, Mikunthan T and Vijayaratnam R. (2001). Some Physio-chemical characters of groundwater in some (selected) water supply wells in the Jaffna peninsula. J. Natn. Sci. Foundation Sri Lanka, Vol. 29, p Sri Lankan Standards 614: part 1(1983). Specification for potable water physical and chemical requirements. p World Health Organization (1984). Guidelines for drinking water quality Vol.1, Recommendations. Geneva. p. 79. Copyright 2013 GSSL 113